Geochemical signatures in Late Triassic brachiopods from New Caledonia

Abstract

Brachiopod fossils from the sedimentary sequences of the Téremba Terrane (New Caledonia) provide a unique opportunity to study the environmental parameters of the Late Triassic. 87Sr/86Sr ratios, δ13C and δ18O values, and Sr/Ca, Mg/Ca and Mn/Ca ratios were measured on brachiopods from Oretian to Otapirian (Norian to Rhaetian) fossil localities of the Baie de St.-Vincent area. Post-depositional impacts on the geochemical proxies were investigated by analysing calcite cements and partly recrystallized shell material. Diagenetic fluids carried strontium with a low 87Sr/86Sr ratio of c. 0.7065, and light δ13C values of c.-20‰, suggesting major contributions by oxidized organic matter. Diagenetic equilibrium was reached at δ18O values of c.-12‰, very low Sr/Ca ratios of < 0.05 mmol/mol and locally variable Mn/Ca ratios of up to 5.9 mmol/mol. Results from the best-preserved samples suggest that calcification temperatures of Warepan and Otapirian brachiopods from New Caledonia were consistently ≥ 15 °C.